Dynamic field time-of-flight mass spectrometer

ABSTRACT

A time-of-flight mass spectrometer which employs a dynamic electric field to accelerate charged particles. For a sample containing various charged particles and given field parameters, each mass-to-charge specie of the sample has associated with it a unique flight time in the dynamic field. This flight time is derived from the interaction of the charged particles with the dynamic field. Various particles are resolved according to their mass-to-charge ratios by recording differences in their flight times in the dynamic electric field.

United States Patent [72] Inventors LowellD. Ferguson 3,527,939 9/1970 Dawson eta]. 250/41.9 DS

" FORElGN PATENTS 1,230,714 9/1960 France 250/419 DS [21 AppLNo. 889,436 [22] Filed Dec. 31, 1969 OTHER REFERENCES [45] Patented Nov. 16,1971 IBM Technical Disclosure Bulletin; Vol. 8, No. 1; June, [73] Assignee TheBendbrCorporatlon 1965;Lever;p. 179.

[54] DYNAMIC FIELD TIME-OF-FLIGHT MASS SPECTROMETER 47 Claims, 15 Drawing Fig.

[52] US. Cl ..250/4l.9 DS, 250/419 TF [51] Int. Cl. H01] 39/36 [50] FieldoiSearch 250/419 lDS, 41.9 TF

[56] References Cited UNITED STATES PATENTS 3,342,993 9/1967 O'Halloran et al. 250/419 TF Ja /i1." 27% M n ,w

7/4 (T or fr /2252a] Primary Examiner-Anthony L. Birch Anorneys-Plante, ll-lartz, Smith and Thompson and Raymond J. Eifler ABSTRACT: A time-of-flight mass spectrometer which employs a dynamic electric field to accelerate charged particles. For a sample containing various charged particles and given field parameters, each mass-to-charge specie of the sample has associated with it a unique flight time in the dynamic field. This flight time is derived from the interaction of the charged particles with the dynamic field. Various particles are resolved according to their mass-to-charge ratios by recording differences in their flight times in the dynamic electric field.

PATENTEnuuv 16 can SHEET 3 (IF 7 4 7 .ffffff, (Tiff w u M I I h 1 1m H I d m 1 r q I Z q a H nd i J A 4 J y m m 7 awe/7 DYNAMIC FIELD TIMEOF-FLIGI'IT MASS SPECTROMETER BACKGROUND OF THE INVENTION 1. Field of the Invention Mass Spectrometers.

2. Description of the Prior Art A number of mass spectrometer designs are well known to thoseskilled in the art. A review of these devices can befound in the book entitled, Dynamic Mass Spectrometers," E. W. Blauth, Elsevier lPublishing Company, New York (1966). The following is a brief description of the spectometers therein described that are most relevant to the subject invention.

In a basic time of flight mass spectrometer, charged particles are accelerated to a selected energy by a pulsed electric field and thereby moved from a source, acrossan electric field-free drift region where they separate according to their mass-to-charge (m/e) ratios, and toward a detector. ions with different m/e ratios are then distinguished by recording their times of arrival at the detector. Those ions with smaller m/e ratios accelerate more rapidly in response to the electrostatic pulse than do ions with larger rn/e ratios. Temporal separation between adjacent m/e species decreases with increasing mass and increases with the length of the drift region.

Another device, called an acceleration spectrometer, indirectly applies thetime of flight principle to achieve mass-tocharge resolution. lons traverse a path of alternately positioned accelerating electric fields and electric field-free drift regions to reach a detector. Voltagepulses are applied to the acceleration regions and are appropriately phased with respect to each other so that only'those ions which arrive at successive acceleration regions at the right times will receive accelerating pulses and reach a detector. Other ions will have m/e ratios such that they will not be propelled by an accelerating pulse to be in proper position to be accelerated toward the detector by subsequent pulses. An example of such a device is a Bennett type mass spectrometer. Resolution in the basic time of flight and acceleration spectrometers is limited by both variations in the kinetic energies and the spatial positions of the ions in the source.

There are also a number of mass spectrometer designs which separate ions according to their m/e ratios by oscillation of the ions in a dynamic electric field wherein only a single m/e species is selected to oscillate with an amplitude sufficiently small to allow such ions to reach a detector. The quadrupole and monopole mass spectrometers are examples of such devices. Ions inserted into the dynamic field of such spectrometers are accelerated by the field to undergo either stable orunstable motion, depending on the m/e ratios of the ion species and the field parameters. ions undergoing stable motion in the field undergo oscillations of limited amplitude. Stable ions, having amplitudes less thanthe physical dimensions defining the boundaries of the dynamic field, reach a detector. Unstable ions undergo oscillations which continually grow in amplitude such that the'unstable ions are lost to the electrodes of the spectrometer and therefore are not detected. The range of stable m/e species is controlled by the dynamic field parameters. Resolution is achieved by adjusting these parameters such that only ions of'a single m/e ratio arestable and only such ions reach the detector.

Aside from stability, the criterion for detection is that the oscillation amplitude which depends also on'the initial conditions, is less than the physical dimensions of the dynamic field. A fringing field extending from the analyzer into the source, experienced by ions as they enter the dynamic field, adversely affects the transmission of the ions in the dynamic field in this type of device. Transmission losses are also encountered owing to the fact that adjustment of the field parameters to stabilize a single m/e specie leads to restrictions on the initial conditions such as the initial positions and energies of ions. The restrictions on the initial ion condition become more severe as resolution is increased.

in a related class of mass spectrometers, a radiofrequency electric field is used to accelerate ions in a static potential well. Only ions with appropriate m/e ratios acquire sufficient energy to escape the static well and be detected. The interaction between the dynamic field and the ions in this spectrometer is identical to that in the previously described dynamic field spectrometer (quadrupole, monopole, etc.). The difference is that in this related class, unstable ions are detected.

Another class of mass spectrometers which. oscillate charged particles to separate them according to their m/e ratios is known as Palletron principle spectrometers. lons oscillate in a static, parabolic electric potential well. The ions interact with the electric field and execute periodic motion of a characteristic frequency determined by their m/e ratios and the field. The applied voltages fonning the potential well are periodically varied to allow selected m/e ratios to escape the potential well. Detection means are provided to observe either the group of ions that have been allowed to escape the well, or to observe those remaining in the well. A shortcoming of this device is that after an appropriate number of oscillations in the well, one m/e specie becomes displaced from another by an oscillation cycle, thereby making it impossible to distinguish between the two species.

SUMMARY OF THE INVENTION The mass spectrometer of this invention includes means for creating a dynamic field which interacts with ions inserted into the field and temporally separates them according to their m/e ratios. The spectrometer includes means for timing the flight of ions in the dynamic field. This spectrometer uniquely resolves charged particles according to their m/e ratios by measuring directly the flight times of ions in the dynamic field. This principle of measurement distinguishes this invention from all other mass spectrometers. As used herein, a charged particle or ion will be any particle with a net electrical charge. As used herein, the tem dynamic electric field refers to an electric field having both a static and an oscillating component or a field having only an oscillating component.

lnthe preferred embodiment illustrated herein, the dynamic field is a dynamic electric field which is symmetric about an axis and includes both a static and a sinusoidally varying field component. A sample of ions is accelerated from a source into the dynamic field along the axis of field symmetry. The static compound acts to draw the ions into the field. The oscillating component of the field alternately works to drive the charged particles with and then against the static component of the field, thus giving the charged particles as complex motion. Depending on the field parameters and the mass-to-charge ratios, the ions are separated into stable and unstable groups as a result of the interaction with the dynamic field. Stable particles are those characterized by oscillatory motion of bounded amplitude. Unstable particlesare those characterized by oscillatory motion of unbounded amplitude. Those stable species whose oscillation amplitudes are less than the physical dimensions defining the boundaries of the field return to the region of injection and strike a detector. For fixed field parameters, each returning m/e specie has a unique time of flight in the dynamic field which will be referred to herein as the characteristic flight time'of that particular specie in that particular dynamic field. Resolution of various species of stable particles according to their m/e ratios is thus achieved by detecting the stable species and recording differences in'their flight times. The unstable particles are lost to the walls of the spectrometer.

The dynamic field parameters include the frequency and the voltage amplitude of the oscillating component of the field, the magnitude of the static field component, and the characteristic field dimensions which define the field geometry. During typical operation, a device of constant geometry is assumed, so that varying the field parameters refers to the frequency of oscillating component, the amplitude of the oscillating component, and the magnitude of the static component. These parameters are adjusted to change the number (range) of We species which undergo stable motion and their relative stability positions. That is, in one test or analysis the field parameters are adjusted so that a particular m/e specie is one of the lightest species undergoing stable mo tion. In another test, the field parameters are adjusted so that the same m/e specie either is among the heaviest species undergoing stable motion or undergoes unstable motion. Changes in both the characteristic flight time for a particular m/e specie in the dynamic field region and the relative differences in the characteristic flight times for different species of ions are accomplished by adjusting the field parameters.

The source parameters include the interval of time during which ions are created, the interval of time during which ions are injected into the dynamic field, the phase of the oscillating field component at which ions are injected into the dynamic field, and the energy of the injected ions. As will be described more fully hereinafter, proper selection and variation of the field and source parameters provide measurements which determine the composition of an ion sample and which are relatively insensitive to variations in both the kinetic energies and spatial positions of the ions in the source.

Several embodiments showing different structures for providing dynamic electric fields and showing different arrangements of ion source apparatus, ion detector apparatus, and means for creating the dynamic field are included herein. Techniques for dynamic field accommodation of ions having differences in kinetic energies and spatial positions at the time of injection into the field are discussed. In one embodiment of the invention, particles can be stored for a selected period of time, thus increasing sensitivity by permitting identical samples to be periodically introduced into the dynamic field to increase the concentration of a stable specie before that specie is detected. I

The wide variety of available dynamic field geometries, source and detector configurations, and means for controlling the field and source parameters in order to obtain different desired results, constitute a major advantage of the present invention. As discussed more fully hereinafter, the time-of-flight measurement in the present invention is relatively insensitive to variations in both the kinetic energy and spatial position of ions in the source. Also, the oscillatory nature of the motion of the ions in the present invention means that the ion paths are spatially folded upon themselves. The advantage of this I folding" is that less analyzing field length is needed to achieve resolution than in other time-of-flight spectrometers.

The continuous interaction in the present invention between ions and the dynamic field provides a separation between various species of ions in which one species of ions cannot spatially overtake another species. This is a distinct advantage over spectrometers based on the Palletron principle.

Also, as will be more fully discussed hereinafter, the timeof-flight measurement made in the present invention improves the m/e measurement over that in such instruments as the monopole, quadrupole, and related devices, which use dynamic fields to separate ions, but rely on only the spatial separation of the ions in the dynamic field to achieve resolution: the time-of-flight measurement in the present invention makes it possible to detect and resolve a range of m/e ratios rather than just a single species of ions in a single test; by the appropriate adjustment of the source and field parameters, a greater transmission of ions through the field is obtained; and ions are introduced into the dynamic field without experiencing fringing fields.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects, features and advantages of this invention will become apparent from a consideration of the following description, the appended claims, and the accompanied drawings in which:

FIG. I is a block diagram of one embodiment of the mass spectrometer of this invention.

FIG. 2 is more detailed of one embodiment of the mass spectrometer of this invention.

FIG. 2 is a more detailed view of the control electronics shown generally in FIG. 1.

FIG. 3 illustrates a portion of the spectrometer shown in FIG. 1 in which the structure for providing a dynamic analyzing field is cut away to show the paths followed by various representative species of ions in the dynamic field.

FIG. 4 is a graph illustrating the 0,, 9, values for ions which undergo motion that is stable in the x, y, and z directions in the dynamic field.

FIG. 5 is a graph illustrating the relationship between particle flight time in the dynamic field and the particle m/e ratio for a selected set of spectrometer operating conditions.

FIG. 6 is a graph illustrating the relationship between particle flight time in the dynamic field and the phase of the dynamic field upon introduction of particlesinto that field.

FIG. 7 is a graph in which the shaded portion of the graph illustrates a, q values which provide bounded solutions to Mathieu's equations and thus indicate stable ion motion in the appropriate direction in the dynamic field.

FIG. 8 is a block diagram of a second embodiment of this invention.

FIG. 9 is a block diagram of that portion of the control electronics of the spectrometer of FIG. 8 which difiers from the control electronics for the spectrometer of FIG. 1.

FIG. 10 illustrates a third embodiment of the spectrometer of this invention.

FIG. 11 is a more detailed view of the programmed optimizing circuit illustrated in FIG. 10.

FIG. 12 is a two-dimensional, schematic view of alternate apparatus for providing a dynamic analyn'ng field of this invention. Stable species of ions enter and exit this field at different points.

FIG. 13 is a second view of the embodiment of FIG. 12 viewed from the plane defined by line 13-13.

FIG. I4 is a diagrammatic view of an embodiment of this invention having ion storage capability.

FIG. 15 is a second view of the embodiment of FIG. [4 as seen from the plane defined by line 15-15. DETAILED, DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Description of the Spectrometer Apparatus FIG. 1 illustrates an embodiment 10 of the mass spectrometer of this invention which includes an analyzing field structure 12 for providing a dynamic electric field which accelerates and decelerates ions thereby temporally separating different m/e ratio species of ions. The spectrometer 10 also includes means 14 for injecting ions into the dynamic field and detector apparatus 16 for detennining and displaying the flight times of various species of ions. Control circuitry 18 controls the operation of the analyzing field structure 12, in introducing means 14, and the detecting apparatus I6. An evacuative envelope 20 surrounds the analyzing field structure 12, the ion introducing means 14 and a portion of the detection apparatus 16.

The means 14 for introducing ions into the dynamic field includes apparatus for ionizing gas particles in the region 22 adjacent to the dynamic field. The apparatus for ionizing gas particles in this region in conventional and includes an electron emitting filament 24 and a control grid 26 for sequencing or determining the times when electrons will flow from filament 24 into the ionizing region 22. An electrostatic focusing lens 28 focuses electron flow through the ionizing region 22. An electrostatic focusing lens 28 focuses electron flow through the ionizing region 22. An anode 30 monitors the intensity of the ionizing electron current. The introducing apparatus 14 also includes a second control grid 32 placed opposite the entrance to the dynamic field to inject ions into that field. A sample gas to be analyzed is introduced into the evacuative envelope envelope 20 and region 22 from a source 34 through valve 36. After the gas sample has been ionized, ions are injected into the dynamic analyzing field by a voltage pulse supplied to this second grid 32.

The apparatus lltS for detecting various separated ion species and for measuring the differences in their relative times of flight is conventional and includes a detector 37 which may be either an electron multiplier or a Faraday cage placed to be struck by ions exiting the analyzing dynamic field, and readout apparatus 3% which comprises a wide band amplifier and an oscilloscope for measuring and displaying the differences in the time of flight for various ion species. The readout apparatus 3h is activated by control circuitry 118.

The analyzing field structure lit for providing the dynamic electric field includes a series of ring-shaped, metal, electric field electrodes 3% and an apertured endclectrode dill having an aperture ill which defines the ion entrance/exit to the dynamic field and a cone-shaped interior surface dill disposed along the z-axis of the spectrometer Ml. Each of the electricfield, ring electrodes 39 has an inside radius of length R." The electric field electrodes are sandwiched between dieletric spacers l3 to which they are fixedly attached to create a rigid structure. Combined ac and dc voltages are applied to the electric-field, ring electrodes 39 from the control electronics Mi through a potential divider M. Electrode 4b is maintained at ground potential.

The construction of the potential divider M and the applied voltages are chosen to provide a dynamic electric field defined by a potential distribution @(x, y, z, t) of the form where z is the longitudinal coordinate and x and y are the radial coordinates of the analyzing dynamic field region; aF=211fis the frequency of the oscillating field, t is time; l dc is the dc component of the electric potential; v is the amplitude of the oscillating component of the electric potential; and G is a geometric constant defined by the equation G L RI2 where L is the length of the analyzing field structure along the z-axis and R is the inner radius of that structure.

The specific apparatus configuration and dynamic electric field distribution described heretofore were chosen solely to illustrate the nature of the invention. The physical arrangement of the structural and field forming elements may be modified. Also, it will be obvious to those-skilled in the art to use other dynamic fields which vary one or more of the characteristics of the previously described dynamic field in practicing this invention. For example, the spectrometer may be operated where v while still achieving mass specie resolution. A more general electric field configuration which can be used in conjunction with the present invention is the field characterized by the potential distribution arbitrary periodic function of time and or, 'y, and n are constants satisfying aPyH QDynamic potential distributions higher than quadratic are also applicable.

The control circuitry id is constructed so that an operator can select a signal of desired strength and frequency to be supplied to the potential divider M, and thus to the electric-field ring electrodes 39. This circuit is also constructed so that a signal of the proper strength will be supplied to the two control grids 26 and 32 at the proper times during operation of the spectrometer.

MG. 2 provides a detailed illustration of the control circuitry l8 which is shown generally in HO. 1. This control circuitry includes a 1 MHz. crystal oscillator 36 which generates a square wave electric signal and thus provides a highly stable time base for the oscillating component of the dynamic field and for the control of grids 2d and 32. The square wave from the oscillator id is transmitted to countdown logic or multistage counter l8. This counter reduces the frequency of the l Mlhlz. signal in order to generate master pulse for initiating a time base for spectrometer operation. The control 48 also reduces the l Ml-lz. signal to generate timing triggers for the control of grids 26 and 32 and to provide a signal of the desired frequency from which the oscillating part of the dynamic field is derived. The dynamic electric field is pro vided by a square wave signal from the countdown logic M which is first transmitted through a low pass filter fill which converts that signal into a sine wave signal. sine wave preamplifier 52 and sine wave power amplifier 3d provide variable gain control in order to obtain the desired amplitude of the oscillating component of the dynamic field. The output signal from the power amplifier M is transmitted not only to the potential divider d4! but also baclt to the preamplifier 52 through a regulator 56. The regulator feedback provides a means for setting the sine wave voltage amplitude at a desired level and for maintaining that amplitude under both line and load variations. The static component of the dynamic electric field is provided by a variable direct current power supply 58.

The control circuit id also includes a pulse generator so which controls the operation of the grid 26, and an ion injection pulse generator M and an ion dnaw outpulse generator dd both or" which control the operation of the grid 32. llulse generator fill, which controls the operation of the grid 3%. Pulse generator which controls the amount of ionization of a sample, is constructed to generate a positive going pulse which is variable in amplitude, width, level, and phase with respect to the master pulse received from the countdown logic 4h. Pulse generator m which controls ion injection into the dynamic field, is constructed to generate a positive pulse which is variable in amplitude, width, and phase with respect to the master pulse received from logic 48. Since both the operation of the generator 62 and the frequency of the oscillating field component are controlled by operation of countdown logic as, the initiation of ion injection and the time interval over which ions will be injected into the dynamic field can be varied as a function of the phase of the oscillating field component. Pulse generator M is constructed to generate a negative going pulse which is variable in amplitude, width, and phase with respect to ion injection pulse in order to accelerate returning ions to a detector 37 (FIG. 1). The output signals from the pulse generators 62 and Ml are both transmitted to a composite pulse generator M which combines the ion injection pulse and the ion drawout pulse into one waveform in order to drive grid 32.

8. Brief Description of Spectrometer Operation The operation of the spectrometer llll shown in H0. l is il lustrated by lFlGS. 3-7. In operation gas sample particles are bombarded by a stream of electrons and ionized by those electrons in the region 22 adjacent the dynamic electric field. (FIG. 1). The stream of electrons is provided by filament 241. The direction and intensity of electron flow through the ionizing region 22 is controlled by the operation of a control grid 26, electrostatic lens 28, and anode 30. After the gas particles have been ionized, they are pulse injected into the dynamic electric field by a voltage pulse supplied to the control grid 32;. The motion of representative species of ions in the dynamic field is shown by the cutaway view of the spectrometer llll of FIG. 3. The dynamic electric field will accelerate and decelerate certain m/e ratio species of ions in a manner such that they will undergo oscillations of unlimited amplitude and be lost to the electrodes of the analyzing field structure 12. That is, these ions follow paths similar to paths oh and 7d and are said to undergo unstable motion in the dynamic field. Other species of ions follow paths similar to path 72, undergo oscillations of limited amplitude such that they do not strike the walls of the analyzing field structure, and return to strike the detector 37. These species of ions are said to undergo stable motion in the dynamic field. The graph of FIG. 3 illustrates that for any particular set of operating conditions, there will be a range of ions that will undergo stable motion in the dynamic field, and a different range of ions that will undergo unstable motion in the dynamic field. All particles lie along the line labeled u" on the graph of HG. B for fixed ratio v /v Add species which fall along that line between the line labeled B=0 and [i=1 will undergo oscillations of limited amplitude in the dynamic electric field.

FIG. illustrates the relationship for fixed operating conditions between ion flight time and ion m/e ratio for particles undergoing stable motion in the dynamic field. As can be seen from FIG. 5, light particles, that is those ions with small m/e ratios which fall nearer the line B 1 than the line B 0 on FIG. 4 return to the detector 37 before the heavier particles having higher m/e ratios. As can be seen from FIG. 5, the differences in the relative flight times for light particles having closely related m/e ratios is smaller than the difference between the flight times for heavy particles having closely related m/e ratios. Since a particular species of ions can be made to undergo either stable or unstable motion or can be either among the lightest or the heaviest of those ions undergoing stable motion in the dynamic field by proper selection of the dynamic field parameters, the resolution between particular species of ions can thus be increased by properly altering the dynamic field parameters. The dynamic field parameters are adjusted by varying the operation of the countdown logic 48 to vary the frequency of the oscillating field component, by adjusting the sine wave preamplifier 52 and sine wave power amplifier 54 to control the amplitude of the oscillating field component, and by adjusting the V power supply 58 to con trol the magnitude of the static field component. With reference to FIG. 4, the flight of a particular species of ions can be altered by changing the operating parameters in a manner which changes the ratio of V to V and thus changes the slope of the u line. The field parameters and the ion flight time can also be changed in a manner which keeps the ratio V JV constant but moves the position of a particular particle on a given u" line.

In addition to the above described operating characteristics of this spectrometer, FIG. 6 illustrates that the time interval during which particles of a particular species strike the detector 37 will be less than the time interval during which particles of that species were injected into the analyzing dynamic field if those particles were injected during a time interval properly chosen with respect to the phase of the oscillating field component. Any particular injection interval can be selected with respect to the phase of the oscillating field component and any particular injection pulse can be obtained by straightforward adjustment of the countdown logic 48 and the injection pulse generator 62 respectively.

C. Detailed Description of the Operation Principles of the dynamic Field Mass Spectrometer 1. Mathematical Parameters A list of symbols used in describing the operating principles of the mass spectrometer are defined as follows:

l =electric potential distribution x,y,z rectangular coordinates r time i velocity in x-direction (first time derivative) i acceleration in x-direction (second time derivative) f frequency of alternating field in cycles/sec. u =27rf= frequency of alternating field in radians/sec rut/2 independent time variable in the Mathieu equations a,q= canonical parameters in the Mathieu equations V amplitude of the ac component of the potential V magnitude of the dc component of the potential L length of the dynamic field region R radius of the dynamic field region G =1. R/ 2 geometric factor m mass of charged particle e electronic charge on the charged particle u a/q ratio of the canonical parameters in the Mathieu equations charge particle flight time in radians r charge particle flight time in seconds The paths followed by charged particles oscillating in the dynamic electric potential distribution of Equation (1) are defined by the following component Mathieu equations in canonical form:

where 2e 1r! 21rft and the parameters a and q are given by 2 46V qlr em (4) 2. Stable and Unstable Charged Particle Motion Depending on the values of the dimensionless parameters a and q, motion described by the Mathieu equation:

is either stable or unstable (bounded or unbounded). FIG. 7 shows one range of a and q values for which stability occurs (shaded portion). Charged particle motion relative to this region of stability is or primary interest in the operation of the dynamic mass spectrometer, although operation is possible for a-q values which define other regions. Values of a, q for which charged particles moving in the x, y plane demonstrates stable motion are defined by the shaded area in the first and fourth quadrants. Values of a, q for which charged particles moving in the z coordinate direction demonstrate stable motion are defined by the shaded area in the second and third quadrants of FIG. 7. Three-dimensional stability values for the parameters obtained by superimposing shaded portions of the second and third quadrants upon the first and fourth quadrant portions. Since the magnitudes of a, and a q differ by a factor of 2, the second and third quadrant portions scale differently than the first and fourth. The combined stability region, FIG. 4, defines values of a I, for which charged particles demonstrate three dimensional bounded motion in the dynamic field. The combined region is of the fonn shown since V may assume either positive or negative values. Corresponding values for 0,, q may be calculated from equations (4). Although the selection of s stable :1, q values ensures that associated charged particles will describe bounded motion, the actual size of the envelope of bounded motion is determined by the initial conditions of the particles as they enter the dynamic field region as well as by the values of a and q.

3. Mass Range Stability For simplicity, only the first quadrant of FIG. 4 is considered. To operate a spectrometer with fixed physical geometry or geometric factor G and dynamic field frequency f, values of V and V are selected which define a mass specie operating line u which passes through the combined stability region of FIG. 4. Through the use of equation (4 each charged particle m/e value is associated with unique values of a,, 1 Since a, q are inverse functions of m/e, the larger m/e ratios lie closer to the a, q origin. The range of mle particles for which the associated a, q values on the operating line :4 lie in the region of combined stability will demonstrate stable motion. Those m/e particles lying on u to the left of the B= 0 line have motion unbounded in the z-coordinate. Those m/e particles lying to the right of the )3 =1 line have unbounded motion in the z-direction.

It can be seen that the a, q location of all m/e particles may be shifted along the operating line 11 by varying the magnitudes of V, and V,,, while keeping V /V, constant. By varying the voltages in this manner, the m/e particles are shifted into or out of the region of combined stability, thus altering the mass range of charged particles which demonstrates stable bounded motion. A repeated, systematic variation of the potentials V, and V forms a basis for scanning the mass specie spectrum. The slope of the mass specie operating line u may be altered by varying the ratio V,,,./ V

This results in altering the mass range of stable charged particles.

4. Charged Particle Time-Of-Flight The important characteristic of the motion of particles which are stable is the time-of-flight behavior of the ions in the dynamic field. For a fixed set of operating parameters each ion specie which is stable has a unique flight time measured from the moment that specie enters the filed at z until it returns to z =0. Since the equations of ion motion are uncoupled, only the injection and timing of the flight in the z-direction need be considered. The general solution to the component equation in z for stable motion is =A ch cos ea) (we) +12%? sin (2n+fi) (Ht.

an W rrantiesourse.)

In order to calculate the flight time g of particles which enter at z=0 and return to F0, the left-hand side of (8) is set to 2(fmr Since the initial velocity and the Wronskian w, are nonzero, determination of is made by setting (c) (1w+o) (o) (1UF+a) Note that the ion flight time am- 42 depends on the m/e of the charged particle, the parameters of the dynamic field through )3 and the coefficients C and on the initial phase of injection but g is independent of initial particle velocity of energy. There is a practical limit to the particle velocity at injection for an analyzing field of finite dimensions. Since the penetration of the particle into the oscillating field is proportional to the velocity, the range of injection velocities is limited. A typical relationship between particle flight time Imp and m/e is set forth in FIG. 5 where the frequency f, the potentials v, and the injection phase 5 are held constant. The arbitrary m/e and I coordinates assume specific scale values when V 6, V and frequency w are selected. it then becomes obvious that the rule scale and the particle flight time r scale may be easily altered using parameters V v and w to achieve a wide degree of flexibility in selecting the range of stable masses, flight times and m/e resolution.

5. Mass Resolution The relationship between Imp and m/e in FIG. 5 shows that the time of flight of the charged particles increases rapidly with m/e. The difference in flight times for adjacent m/e values also increases with mass. This favorable situation exists for m/e values which lie on a u line passing through region of stability and which approaches the [i=0 line or the left 2 instability edge of the stability diagram. As the mass species become increasingly separated in time with increasing mass, another characteristic of the Mathieu ac combines to enhance m/e resolutions. Particles which enter the ac field at zz=o over a period A5,, are bunched in time during interaction with the ac field and return in a time period Af which is shorter than Ag This time bunching is illustrated determined as a function of the tion for fixed values ofa and 6. Mass Scanning One method for displaying a resolved mass spectrum if the mass range is not too large requires that all charged particle species be located within the combined stability diagram simultaneously through proper selection of the v and v potentials and operating frequency w. The mass spectrum may be displayed on an oscilloscope for each analysis cycle.

A second display technique measurement of the arrival of ions at the detector 37 at a preselected time and the programmed increase or decrease of V and V. to succwsively alter the rn/e specie flight times in such a manner that each specie will achieve the preselected flight time in sequence. An example of this technique is illustrated in lFlG. l where the voltage ratio Fil adv and w are held constant and all mass species lie on this u line which passes through the stability diagram. in reality, each a q, point on the s stability diagram is associated with a unique 5 The preselected flight time is written as I' =2 g' lmwhere a'uniq'ue mp is associated with a and q if V, and V. are adjusted so that mass m., is positioned at a and 1' as shown in FIG. 5, then m: and m will have shorter flight times then t mp. Also, m, and m are unstable. As V and V are increased, m will be moved toward a 1' where its flight time will be t mp. As V 0M l/ are decreased, m m and m are successively moved to the point a' q' and succmively appear in. the mass-time spectrum at I mp.

A sequential of all mass species in a gas sample may be achieved by a narrow time gate about r' at the output of the detector-multiplier. The current output through this narrowtime gate provides a display of the mass specie spectrum as the potentials V and V are varied in either an increasing or decreasing manner while keeping 2 l /l constant.

Other techniques are available for scanning the mass spectrum. The frequency a: of the ac field may be continuously altered to move each mass specie through the point 0' 11' D. Alternate Embodiments of this invention FIGS. 8-14 illustrate alternate embodiments to this invention. The following description of directed toward pointing out the structural and operational differences between these embodiments and the spectrometer W. No detailed description is provided for structural elements of these alternate embodiments which also appear in the spectrometer i0 and have already been completely described. These elements are labeled in each drawing with the numeral used to designate the corresponding element of the spectrometer Ml.

lFlG. illustrates a spectrometeT'i l which differs from the spectrometer ill in that sample gas particles to be analyzed are introduced from the gas source M through a tube 76 directly into the ionizing region 22. Gas particles can thus be immediately ionized and then injection into the dynamic analyzing field with minimum drift of neutral gas particles around in the evacuative envelope E0. The spectrometer Ml also differs from spectrometer it) in that the ring shaped electric-field electrodes 39 and dielectric spacers d3 are replaced by a single, tubular shaped resistive electrode structure 7%. The electrical resistance of any particular portion of the resistive electrode 78 is selected so that when a potential is applied to one end of that electrode from control circuitry fill through lead 82, a proper analyzing field such as that obtained from potential distribution defined by equation (2) will be provided within the volume defined by electrode 73. The control circuitry as, a portion of which is shown in detail in FIG. 9, differs from the control circuitry 18 in that it includes a rectifier 84 for providing the static component of the dynamic electric field. The rectifier 34 receives an alternating sine wave from the power amplifier M and converts it into a dc voltage. Since the sine wave power amplifier 54 provides the input to the rectifier and also determines the amplitude of the oscillating field component, adjusting the gain of the power amplifier in FIG. 6 where is injection phase from equaq.

will vary the dynamic field parameters in a manner which maintains a constant ratio between v and v FIG. illustrates another embodiment 86 of the spectrometer of this invention which includes a Spiraltron electron multiplier detector 88 for detecting species of ions tlnat have been resolved by the spectrometer apparatus. The spectrometer 86 also includes a grounded, cone-shaped electrode 90 and a conducting electrode 92 having a surface 93 which defines a hyperboloid of revolution for providing a dynamic analyzing field. These shapes are such to give a potential distribution of the form of Equation 2. A proper electric signal is supplied to the conductor 92 to provide the dynamic electric field within the volume defined by the conductor 92 and-cone 90 from a programmed optimizing circuit 94. The optimizing circuit also controls ionization and ion introduction into the dynamic field by controlling the operation of grids 26 and 32. In this respect, the circuit 94 is similar to the control circuits l8 and 80.

In addition, programmed optimizing circuit 94 also includes electronics (FIG. 11) for optimizing sigrnals representing the various ion species and for measuring those optimized signals. That is, the programmed optimizing circuit 94 is constructed to maximize the resolution of or separation between signals representing adjacent ion species in one series of tests, and to maximize the strength of the signals representing the various species in another series of tests.

To accomplish this signal optimization, circuit 94 includes a master control or logic circuit 96, apparatus 98 for determining maximum signal values, and signal processing apparatus 100. Master control 96 is programmed to control the ion source and dynamic field parameters and also to receive and respond to pulses from other parts of the programmed optimizing circuit 94 to thereby control operation of circuit 94. Apparatus 98 is constructed to receive and compose various sigrnals from detector 88 to determine the maximum values of these signals. The signal determining apparatus 98 includes signal measuring apparatus 102 which receives and measures signals from the Spiraltron detector 88 caused by ions striking that detector. A threshold circuit 104 presets a minimum signal threshold level so that the measuring apparatus 102 will only measure values above the threshold and thereby avoid the measurement of spurious noise signals. When a signal value above the preset threshold is detected, it is stored in memory 106. if a signal is already stored in memory 106, the newly detected signal will be compared with that stored signal by comparator 108 and only the larger of the two signals will be stored in memory 106. After all signals of interest for a particular operation have been received and measured by apparatus 98, the largest or maximum received signal will have been stored in memory 106. This maximum signal is transmitted through an AND gate whose operation is controlled by the master control 96 to the signal readout apparatus 38 at an appropriate time.

The processing apparatus 100 is constructed to determine and store the field parameters, corresponding to the maximum signal value for a particular ion species and the maximum signal thus provided. Apparatus 100 is also constructed to determine the maximum resolution or separation between signals representing adjacent species of ions. Maximum resolution exists when the difference between the V value that provides a maximum ion signal value for a first species of ions and the V value that provides a maximum ion signal value for a second species of ions is maximized. To accomplish these functions, the apparatus 100 includes a v /v control circuit 112 for varying the dynamic field parameters. This circuit may be similar to either the control circuit of FIG. 2 or that of FIG. 9. The values of the amplitude of the oscillating field component (v provided by adjustment of control 112 are measured by a voltage measuring apparatus 114 and are stored in shift register 1 16. Whenever a maximum signal value is detected by comparator 108, botln that signal value and the v which provided that signal value are transmitted to a memory unit 118. Memory 118 is capable of storing a large quantity of information representing all ion species contained by the sample being resolved. Comparisons and differences which uses that difference value to direct further operation of the programmed optimizing circuitry.

The preferred mode of operation of the spectrometer 86 and optimizing circuitry 94 comprises a mass scanning operation in which only those signals produced by ions striking the detector 88 at a preselected time are measured. Identical ion samples are injected into the dynamic analyzing field in a series of tests. The dynamic field parameters are varied before each test to vary ion flight time. In operation, master control 96 initiates ionization by controlling the operation of pulse generator 60; controls the operation of control 112 to vary V..- and V according to a preset program; and directs measuring apparatus 102 to measure output sigrnals from detector 88 only at a preselected time relative to the ionization time. When the output signal from detector 88 reaches the threshold level established by circuit 103, that detector output value is stored in memory 106. In a subsequent test, the signal value obtained by providing a small change to the scan V and V values is then compared in comparator 108 with the value previously stored in memory 106. If larger, it replaces the stored signal value. This process is repeated as V and V are scanned or varied according to the program until the incoming signal from detector 88 is less than that stored in memory 106, at which time the stored signal is transferred to memory 118. This signal stored in memory 118 will be referred to hereinafter as a peak height and represents the maximum obtainable signal value for a given set of source parameters and for field parameters falling within a given, small range. Simultaneously, comparator 108 sends a pulse to the shift register 116 which directs that register to index the measured V value corresponding to the maximum peak height into memory 118. The mass scanning and signal comparing then continues until the peak heights of a second mass or ion species is similarly processed.

Once the height for two adjacent mass peaks are identified, the scan is interrupted and the measured V, for the two peaks are passed into the subtractor 120 where their difference is taken. This difference together with the associated operating parameters is stored in memory 118. Master control 96 then directs signal measurements at a new detection time by changing the source and field parameters to appropriate new values. The mass scanning loop is then recycled to scan the same two masses again. The resulting V, difference is compared with that previously stored in memory 118 by comparator 122. If greater, this difference together with the associated operating parameters replaces the stored information in memory 118. The variation of operating parameters continues until program completion at which time the master control directs the source and operating parameter controls to adjust to those values identified as corresponding to the maximum V, difference. Maximum resolution has thus been achieved for these masses. The AND-gate 110 then activates the readout 38 and directs the V /V control 112 to scan through the resolved peak. Readout 38 displays this scan.

If, during the process of maximizing resolution, a new mass peak appears between two previously identified peaks, the optimizing circuitry 94 is directed by master control 96 to resolve the first of the former peaks and the new peak. This is continued until the two peaks are best resolved.

During operation, memory 118 is constantly being updated with the maximum peak heights for each of the two masses being resolved along with their associated operating parameters. After achieving maximum resolution, the master control 96 returns to the operating parameters stored in memory 118 which generated the maximum peak height obtained for the first mass while maximizing resolution. The source and field parameters are then indexed according to the program and the measured peak height for each index is compared with that of the previous index. If greater, the more recent index peak height updates the memory 118. Upon completion of the program, the maximum peak height is transmitted to readout apparatus 38 and the peak height maximizing process is then repeated for the second of the two resolved peaks, and then the next one to follow and so on until a complete scan of the mass spectrum is obtained. A ,7

FIGS. 12 and 13 illustrate two views of an additional embodiment 126 of this spectrometer which differs from previously described embodiments in that it includes alternate apparatus 128 for providing an analyzing dynamic field. The analyzing field apparatus is a monopole structure which includes a rod-shaped conducting electrode 130 having a surface 131 which may be either cylindrical or hyperbolic, and two grounded, converging surfaces 132 and 134 spaced a distance from rod 130 and also spaced a distance from each other in order to establish-a slit or gap 136 through which ions enter and exit the dynamic analyzing field. When an appropriate signal having a V or oscillating component is supplied from the control circuitry 18 to the rod electrode 130, a dynamic electric field of the form i (x, y, z, r)=flt)- l/Z,,(y z where:

x, y, z are spatial coordinates along the directions indicated on H68. 12 and 13 and Z, is the length of thedynamic field along the z axis provided in the region bounded by rod 130 and surfaces 132 and 1134.

The field defined by equation (11) is similar to previously defined dynamic fields in that it will accelerate the decelerate and thereby temporally separates various species of ions injected into that field according to their m/e ratios. The field of equation (I l) differs from previously defined fields in that it includes no component along the X-axis. Therefore, if ions which undergo stablemotion in the dynamic field are injected into that field having a component of motion along the x-axis, their direction of motion along that axis will not be reversed by the dynamic field. The means 14 for introducing ions into the dynamic analyzingfield is oriented in the spectrometer 126 to provide ions with a component of motion along the xaxis. Since the dynamic field will not cause the ions to reverse their direction of travel along that axis, the detector 37 is spaced a distance from the introducing apparatus 14 along the x axis. Ions exiting the dynamic field will therefore not have to pass through the introducing apparatus 14 in order to read the detector 37.

FIGS. 14 and 15 illustrate two views of an embodiment 138 of the spectrometer of this invention having ion storage capability. Spectrometer 138 differs from spectrometer in that it includes two identical structures 12 and 140 for providing dynamic analyzing fields. The field structures 12 and 140 are opposed to and axially aligned with each other. The field provided by structure 140 is a mirror image of the field provided by structure 12. lens which undergo stable motion in such a field will therefore oscillate back and forth from one field to another and thus be stored by the spectrometer 138. Stored ions are removed from the dynamic field and accelerated'to the detector 37 by voltage pulses supplied to a grid 142 which is shown only in FIG. to avoid the inclusion of possibly confusing detail in FIG. 14. The operation of grid 142 is controlled by control circuit 144 which is similar to the control circuit 18 but also includes countdown logic and a pulse generator for controlling the operation of grid 142. This additional apparatus is similar to the illustrated apparatus for controlling the operation of grids 26 and 32.

Several modes of operation are possible with the spectrometer 138. As was the case with previous embodiments, a number of different ion species will undergo stable motion in the dynamic field simultaneously. If desired, all stable or stored species can be extracted from the dynamic field in one continuous time interval and resolved by measuring the differences in the times at which the various species strike the detector 37. To accomplish this, a signalwhich ejects ions from region 22 to the detector 37 is simply supplied to grid 142 and maintained on that grid as successive ions enter region 22. Or, in a second mode of operation, selected m/e ratio species can be individually extracted from the dynamic field by transmitting extracting voltages to grid 142 only at those times when the selected species of ions are in region 22. Similarly, a single species of ions can be stored by spectrometer 138 by activating grid 142 to eject ions from the dynamic field at all times except during the time intervals in which that one selected species to be stored passes through region 22. During these time intervals, no signal is supplied to grid 142 so that the motion of this species in the dynamic field will be unaffected. In this way, all species except one selected species of ions are rejected from the resolving dynamic field. The intensity of this species can be enhanced to facilitate detection of that species by periodically injection additional ion samples containing many species of ions intothe dynamic field at times when the previously stored ions are in region 22. Unwanted species are extracted from the field by again activating grid 142 at times selected to eject all but the preselected species of ions from the field. When a suflicient concentration of ions is obtained, grid 142 is activated to accelerate the selected, concentrated species to detector 37. The time, of storage of ions of several species is that determined by the time it takes the ions of one specie to spatially overtake the ions of another specie due to the difference in their flight times equaling one cycle of oscillation about the region 22.

It is believed that the above described detailed description of the preferred embodiments of this invention will. suggest a great number of straightforward modifications to those skilled in this art. For instance, it is clear that the structural elements that are well known in the art such as the ionizing and injecting apparatus 14 illustrated in FIG. 1 can be replaced with other .well known structural elements for performing the same function. In addition, a particular structural element shown in one embodiment can also be used with the apparatus shown in other embodiments. For example, the programmed optimizing circuit 94 need not only be used with an analyzing field structure including a groundedcone and a conductor having a hyperbolic surface as is shown in FIG. 10 but can also be used with a spectrometer having structure such as the apparatus 12 illustrated in FIG. 1 for providing a dynamic and analyzing field. Electrodesl32 and 134 shown in FIGS. 12 and 13 can be a single electrode with appropriated slots for entrance and exit of ions. Or, the detector 37 in the embodiment of FIG. 14 and l5 can also be placed on the z-axis at the outer end of either structure 12m 140. In this design, ions are accelerated to the detector 37 after a selected time of oscillation by voltage supplied to grid 32. To aid their flight to the detector 37, the signal to the ring electrodes 39 may be turned ofi'. Hence these and oth r modifications will be obvious to those skilled in the art.

What is claimed is:

ll. A device for analyzing char particles according to their mass-to-charge ratios comprising:

an evacuable vessel;

a means for creating a dynamic field within said vessel, said dynamic field having a potential with at least two components for accelerating, decelerating and temporally separating various charged particle species according to their mass-to-charge ratios, said dynamic field being periodic in time;

means for introducing field; and

means for measuring a time of flight of said temporally separated charged particle species traveling in the directions of said components.

2. The combination of claim 1 in which said evacuable vessel includes means for directly introducing sample particle species into said means for introducing particles into said dynamic field.

3. The combination of claim 1 in which said dynamic field is further defined by an electric potential distribution of the general quadratic form I (x, y, z, z)=f(.r) (ax -l-yy +nz) where x, y, z are rectangular space coordinates, t is time, a-y, 1; are constants satisfying the relation r+-y-i-q==0, and flt) is a time varying function.

4. The combination of claim 1 in which said means for introducing charged particles into the dynamic field region include means for ionizing gas sample species and means for pulse injecting charged particles into the dynamic field.

charged particles into the dynamic 5. The combination of claim 1 in which said means for measuring a flight time includes means for initiating the timing at a preselected point in the travel of said charged particles and detection means for providing an output signal denoting the time of arrival of said temporally separated particles at a preselected point.

6. The combination of claim 1 further including means for varying the field parameters of said dynamic field.

7. The combination of claim 6 in which said means for creating a dynamic field is constructed to provide an electric field having both an oscillating and a static component and in which said varying means is constructed to vary the amplitude of said oscillating component and the magnitude of said static component both independently of each other and in a manner which maintains a fixed ratio between said amplitude and said magnitude.

8. The combination of claim 6 in which said means for varying the field parameters of said dynamic field is constructed to select different ranges of mass-to-charge species that will demonstrate stable motion in said field, to change the temporal separation between mass-to-charge ratio species, and to alter the characteristic flight times of stable mass-to-charge species.

9. The combination of claim 8 in which said measuring means includes:

detecting means having electron multiplier means and ap propriate electronic means for producing output signals representing the arrival time at the detector of the various temporally separated charge particle species;

electronic means for measuring the lapsed time between charged particle introduction into the dynamic field and the arrival of the various temporally separated charged particle species at said detecting means; and

electronic means for displaying substantially simultaneously all of said output signals, thereby displaying a mass-tocharge spectrum of temporally separated species arriving at said detecting means.

10. The combination of claim 9 in which said introducing means is constructed to periodically introduce charged particles into said dynamic field for the purpose of performing a series of tests; and

further including control means responsive to said simultaneous signals to control said charged particle introducing means, said field parameter varying means, and said measuring means to change from said simultaneous display to an optimized sequential display of selected individual output signals of said simultaneously displayed signals.

11. The combination of claim 6 in which said introducing means includes means for periodically introducing charged particles into the dynamic field for purposes of performing a series of tests; said measuring means is constructed to detect only charged particles having a flight time within a selected range of times of flight; and

in which said means for varying the parameters in subsequent tests, each mass-to-charge species introduced into the dynamic field with a flight time within said selected range of time of flight, thereby achieving a mass scan of said charged particles.

12. The combination of claim 11 in which said measuring means is constructed to cooperate with said means for varying the parameters of the dynamic field and with said introducing means to provide an optimized, sequential display of output signals representing the various mass-to-charge species introduced into said field.

13. A device for analyzing charged particles according to their mass-to-charge ratios comprising:

an evacuable vessel, having means for the introduction of sample particle species into said vessel for analysis; means for creating a dynamic electric field for accelerating and temporally separating various charged particle species according to their mass-to-charge ratios and for providing a characteristic flight time to at least certain of ponent being periodic in time and of the form 0(x, y, z, r)f(Ar)(ou-l-yy'-+nz') where x, y, and z are spatial coordinates, r is time, :(r) is a time varying function, and a, y, 1 constants satisfying the relation a-Py-Hr-O; means for introducing charged particles into said dynamic field, said introduction means constructed to operate periodically in time;

means for measuring said characteristic flight times of temporally separated charged particle species traveling in a direction of one of said coordinates.

14. The combination of claim 13 in which said means for creating a dynamic field include a plurality of conducting, electric-field electrodes and appropriate electric connecting means.

15. The combination of claim 13 in which said means for creating a dynamic electric field include a continuous resistive electrode constructed to form a boundary of said dynamic field.

16. The combination of claim 13 further including means for varying the field parameters of said dynamic electric field.

17. The combination of claim 16 in which said means for creating a dynamic electric field is constructed to provide a field having an oscillating and a static component and in which said varying means is constructed to vary the amplitude of the oscillating component and the magnitude of the static component both independently of each other and in a manner which maintains a fixed ratio between said amplitude and said magnitude.

18. The combination of claim 13 in which said measuring means includes an electron multiplier and appropriate electronics for producing suitable output signals associated with the arrival at the detector of the various temporally separated charged particle species.

19. The combination of claim 18 in which said means for measuring the characteristic flight times of said temporally separated charged particle species includes suitable electronic means for measuring the lapsed time between the time of charged particle injection into the dynamic field and the arrival of the various temporally separated charged particle species at said detector.

20. A device for analyzing charged particles according to their mass-to-charge ratios comprising:

an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis;

means for creating a dynamic electric field within said evacuable vessel, said field being symmetric about an ax'm, periodic in time, and of a form which acts to accelerate, decelerate and separate charged particles into a first group of species having stable motion in the dynamic field, and a second group of species having unstable motion in said dynamic field, said field also being of a fonn to provide a component of motion to said charged particles generally parallel to said axis to accelerate, decelerate and to temporally separate said charged particles according to their mass-to-charge ratios and to provide a unique flight time in said dynamic field for each of said stable charged particle species for selected dynamic field parameters;

means located adjacent the coordinate origin of said dynamic electric field for periodically introducing charged particles into said dynamic field along said axis of symmetry, said axis of symmetry extending through said introducing means;

means for varying the field parameters of said dynamic field; and

means for measuring a time of flight of said temporally separated charged particle species that travel in a direction of said dynamic field.

21. The combination of claim 20 in which said field is of the form d (x, y, z, t)=flt)(a.x-l-yy'-+-nz) where x, y, and z are spatial coordinates, t is time, flt) is a time varying function, and a,

said charged particle species, said field having one com- 'y, 1; are constants satisfying the relation a-l-y-H O.

22. The combination of claim 21 in which said means for creating a dynamic electric field are constructed to produce an electric potential distribution of the form:

where x, y, z are space coordinates, the z-axis of said axis of symmetry, t is time, to is the frequency of the periodic field, V, is the direct current potential, V is the amplitude of the alternating current potential, L is the characteristic length of the dynamic field region as measured from the coordinate origin, and R is the characteristic radius of the dynamic field region as measured from the z-axis.

23. The combination of claim 22 in which said means for creating a dynamic electric field include a plurality of conducting electrodes spaced along said axis of symmetry, and appropriate electric connecting means.

2d. The combination of claim 22 in which said means for creating a dynamic electric field include a continuous resistive electrodeconstructed to form a boundary of said dynamic field.

25. The combination of claim 20 in which said measuring means include charged particle detecting means located on said axis of symmetry.

26. The combination of claim 25 in which said detecting means is positioned such that said introducing means is located on said axis of symmetry between said detecting means and said dynamic field.

27. The combination of claim 20 in which said charged particle introducing means includes:

means for periodically producing charged particles from neutral gas samples;

electronic means for controlling the time interval of charged particle production; electronic means for controlling the energy of the charged particles at introduction into the dynamic field;

means for selecting the time at which said introduction is initiated when the phase of said oscillating component possesses a selected value; and

electronic means for controlling the time interval of charged particle injection into the dynamic field.

28. A device their mass-to-charge ratios comprising:

an evacuable vessel having means for the introduction of sampie particle species into said vessel for analysis;

means for creating a dynamic electric field within said evacuable vessel for accelerating and temporally separating various charged particle species according to their mass-to-charge ratios, said field being of the fon'n @(x, y, z)=flt)( IIZ Xy Z where x, y and z are spatial coordinates, t is time, f(t) is a time varying function, and Z. is equal to the length of the dynamic field along the z-axis;

means for periodically introducing charged particles into the dynamic field with components of motion both in the x and 2 directions; arid means for measuring the flight times of said temporally separated charged particle species that travel in a direction of said dynamic field.

29. The combination of claim 28 in which said dynamic electric field creating means includes a plurality of conducting, electric-field electrodes and appropriate electric connecting means.

, 30. The combination of claim 28 troducing charged vicinity of z=0.

31. The combination of claim 28 in which said measuring means includes charged particle detection means located in the vicinity of z= and is spaced from said introducing means a distance along the x-axis,

in which said means for inparticle into said field is located in the for analyzing charged particles according to v 32. The combination of claim 29 further including means for varying the field parameters of said dynamic field.

33. in the combination of an apparatus for separating charged particles according to their mass-to-charge ratio of the type having an evacuable vessel; elongated electrodes positioned in said vessel and disposed in spaced relationship along a common axis and defining a space therebetween; means for generating a first voltage 1 having an arbitrary periodical function of time flt); means for supplying said first periodical voltage to said elongated electrodes to establish a first electric field between said electrodes having a time periodical field potential which is a general quadratic function M K 'YY W of the rectangular coordinates x, y, z of. the elongated electrode arrangement, a, y, 1 being constants satisfying the equation when means for introducing charged particles into said electric field between said elongated electrodes so that the forces of said first field are exerted on said charged particles to cause certain charged particles to perform oscillations of a limited amplitude and others to perform oscillations of an increasing amplitude depending on the respective specific charges of the charged particles, the improvement comprising: means for establishing a second electric field in the space between said elongated electrodes, said second electric field having a time periodical field potential having a component in said z direction of said first electric field so that the force of said second electric field exerted on said charged particles between said electrodes cause said particles to oscillate the z-directionr whereby theduration of time that said charged particles introduced into said field perform oscillations in the x and y-directions between said elongated electrodes is a function of said second electric field.

34 A device for analyzing and storing charged particles according to their mass-tocharge ratios comprising:

an evacuable vessel including means for introducing sample particles into said vessel for analysis;

means for creating a dynamic electric field within said evacuable vessel, said field being; periodic in time, and of a form which acts to accelerate and separate charged particles .intoa first group of species having stable motion in said dynamic field and a second species group having unstable motion in said dynamic field, said-field also being of a form to temporally separate said stable species according to their mass-to-charge ratio and restore certain of said stable species;

means for introducing charged particles into said dynamic field, said charged particle introducing means located adjacentto the coordinate origin of said dynamic electric field and includes:

means for producing charged particles from neutral gas samples;

electronic means for controlling the time interval of charged particle production;

means for controlling the kinetic energy of the charged particles upon introduction into the dynamic field;

means for selecting the time at which said introduction is initiated relative to the phase of said oscillating component; and

means for controlling the time interval of charged particle injection into the dynamic field;

means including timing means for removing selected stable species from said dynamic field; and

means for detecting stable species stored in said dynamic 35. The combination of 34 in which said charged particle introducing means is constructed to periodically produce and periodically inject charged particles into said dynamic field.

36. The combination of claim 34 in which said means for removing selected stable species from said dynamic field is constructed to remove all but one of the selected stable charged particle species from said field.

37. The combination of claim 34 in which said removing means is constructed to periodically remove selected stable species from said dynamic field.

38. The combination of claim 34 in which said charged particle introducing means and said removing means are constructed to act together to cause the concentration of a selected stable mass to charge ratio species of charged particles contained in said dynamic field to increase.

39. The combination of claim 38 in which said detecting means includes timing apparatus and is constructed to cooperate with said removing means to remove said concentration of said stored species after a preselected time.

40. The combination of claim 34 in which said means for creating a dynamic electric field are constructed to produce an electric potential distribution of the form i (x, y, z, t)=fl t)(ax'+'yy,+1 z) where x, y, z are spatial coordinates, t is time,

fl!) is a time varying function, and a, 1 are constants satisfying the relation a-Py-H O.

41. The combination of claim 40 in which said means for creating a dynamic electric field are constructed to produce an electric potential distribution of the form:

where the z-axis is said of axis of symmetry, in is the frequency of the periodic field, V, is the magnitude of the static field component, V is the amplitude of the oscillating field component, the length of the dynamic field region is 2L, and R is the characteristic field radius, and all other quantities are as previous defined,

said field also being symmetric through the plane F0.

42. The combination of claim 41 further including means for varying the field parameters of said dynamic field.

43. The combination of claim 42 in which said means for varying the field parameters of the dynamic field is constructed to select different ranges of mass-to-charge species that will demonstrate stable motion and will be contained in this field, and to change the temporal separation between various stable species.

44. A device for analyzing charged particles according to their mass-to-charge ratios comprising:

an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis;

means for creating a dynamic electric field within said evacuable vessel, acting to accelerate, decelerate and separate charged particles into a that group of species having stable motion in the dynamic field and a second group of species having unstable motion in said dynamic field, said field also providing a component of motion to said charged particles generally parallel to said axis to accelerate, decelerate and to temporally separate said charged particles according to their mass-to charge ratios and to provide a unique flight time in said dynamic field for each of said stable charged particle species for selected dynamic field parameters, said field of the form (x, y, z, t)=flt)(ax*-l'yy*-l-nz') where x, y, and z are spa tial coordinates, t is time, flt) is a time varying function, and a, y, 1 are constants satisfying the relation a-PyH O and wherein said means for creating a dynamic electric field is constructed to produce an electric potential distribution of the form 1 w +y L52 2 where x, y, z are space coordinates, the z-axis is said axis of symmetry, t is time, to is the frequency of the periodic field, V is the direct current potential, V is the amplitude of the alternating current potential, L is the characteristic length of the dynamic field region as measuredtromthecoordinateori n andRisthecharacteristic radius of the dynamic eid region as measured from the z-axis;

means located adjacent the coordinate origin of said dynamic electric field for periodically introducing charged particles into said dynamic field along said axis of symmetry, said axis of symmetry extending through said introducing means;

means for varying the field parameters of said dynamic field; and

means for measuring a time of flight of said temporally separated charged particle species for flight including motion in said dynamic field.

45. The combination of claim 44 in which said means for creating a dynamic electric field include a plurality of conducting electrodes spaced along said axis of symmetry and appropriate electric connecting means.

46. The combination of claim 44 in which said means for creating a dynamic electric field include a continuous resistive electrode constructed to form a boundary of said dynamic field.

47. A device for analyzing charged particles according to their mass-to-charge ratios comprising:

an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis, said charged particle introducing means including:

means for periodically producing charged particles from neutral gas samples;

electronic means for controlling the time interval of charged particle production;

electronic means for controlling the energy of the charged particles at introduction into the dynamic field;

means for selecting the time at which said introduction is initiated when the phase of said oscillating component possesses a selected value; and

electronic means for controlling the time interval of charged particle injection into the dynamic field;

means for creating a dynamic electric field within said evacuable vessel, said field being symmetric about an axis, periodic in time, and of a fonn which acts to accelerate, decelerate and separate charged particles into a first group of species having stable motion in the dynamic field, and a second group of species having unstable motion in said dynamic field, said field also being of a form to provide a component of motion to said charged particles generally parallel to said axis to accelerate, decelerate and to temporally separate said charged particles according to their mass-to-charge ratios and to provide a unique flight time in said dynamic field for each of said stable charged particle species for selected dynamic field parameters;

means located adjacent the coordinate origin of said dynamic electric field for periodically introducing charged particles into said dynamic field along said axis of symmetry, said axis of symmetry extending through said introducing means;

means for varying the field parameters of said dynamic field; and

means for measuring a time of flight of said temporally separated charged particle species for flight including motion in said dynamic field. 

1. A device for analyzing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel; a means for creating a dynamic field within said vessel, said dynamic field having a potential with at least two components for accelerating, decelerating and temporally separating various charged particle species according to their mass-tocharge ratios, said dynamic field being periodic in time; means for introducing charged particles into the dynamic field; and means for measuring a time of flight of said temporally separated charged particle species traveling in the directions of said components.
 2. The combination of claim 1 in which said evacuable vessel includes means for directly introducing sample particle species into said means for introducing particles into said dynamic field.
 3. The combination of claim 1 in which said dynamic field is further defined by an electric potential distribution of the general quadratic form phi (x, y, z, t) f(t) ( Alpha x2+ gamma y2 + eta z2) where x, y, z are rectangular space coordinates, t is time, gamma , eta are constants satisfying the relation Alpha + gamma + eta 0, and f(t) is a time varying function.
 4. The combination of claim 1 in which said means for introducing charged particles into the dynamic field region include means for ionizing gas sample species and means for pulse injecting charged particles into the dynamic field.
 5. The combination of claim 1 in which said means for measuring a flight time includes means for initiating the timing at a preselected point in the travel of said charged particles and detection means for providing an output signal denoting the time of arrival of said temporally separated particles at a preselected point.
 6. The combination of claim 1 further including means for varying the field parameters of said dynamic field.
 7. The combination of claim 6 in which said means for creating a dynamic field is constructed to provide an electric field having both an oscillating and a static component and in which said varying means is constructed to vary the amplitude of said oscillating component and the magnitude of said static component both independently of each other and in a manner which maintains a fixed ratio between said amplitude and said magnitude.
 8. The combination of claim 6 in which said means for varying the field parameters of said dynamic field is constructed to select different ranges of mass-to-charge species that will demonstrate stable motion in said field, to change the temporal separation between mass-to-charge ratio species, and to alter the characteristic flight times of stable mass-to-charge species.
 9. The combination of claim 8 in which said measuring means includes: detecting means having electron multiplier means and appropriate electronic means for producing output signals representing the arrival time at the detector of the various temporally separated charge particle species; electronic means for measuring the lapsed time between charged particle introduction into the dynamic field and the arrival of the various temporally separated charGed particle species at said detecting means; and electronic means for displaying substantially simultaneously all of said output signals, thereby displaying a mass-to-charge spectrum of temporally separated species arriving at said detecting means.
 10. The combination of claim 9 in which said introducing means is constructed to periodically introduce charged particles into said dynamic field for the purpose of performing a series of tests; and further including control means responsive to said simultaneous signals to control said charged particle introducing means, said field parameter varying means, and said measuring means to change from said simultaneous display to an optimized sequential display of selected individual output signals of said simultaneously displayed signals.
 11. The combination of claim 6 in which said introducing means includes means for periodically introducing charged particles into the dynamic field for purposes of performing a series of tests; said measuring means is constructed to detect only charged particles having a flight time within a selected range of times of flight; and in which said means for varying the parameters in subsequent tests, each mass-to-charge species introduced into the dynamic field with a flight time within said selected range of time of flight, thereby achieving a mass scan of said charged particles.
 12. The combination of claim 11 in which said measuring means is constructed to cooperate with said means for varying the parameters of the dynamic field and with said introducing means to provide an optimized, sequential display of output signals representing the various mass-to-charge species introduced into said field.
 13. A device for analyzing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel, having means for the introduction of sample particle species into said vessel for analysis; means for creating a dynamic electric field for accelerating and temporally separating various charged particle species according to their mass-to-charge ratios and for providing a characteristic flight time to at least certain of said charged particle species, said field having one component being periodic in time and of the form phi (x, y, z, t) f(t)( Alpha x2+ gamma y2+ eta z2) where x, y, and z are spatial coordinates, t is time, f(t) is a time varying function, and Alpha , gamma , eta constants satisfying the relation Alpha + gamma + eta 0; means for introducing charged particles into said dynamic field, said introduction means constructed to operate periodically in time; means for measuring said characteristic flight times of temporally separated charged particle species traveling in a direction of one of said coordinates.
 14. The combination of claim 13 in which said means for creating a dynamic field include a plurality of conducting, electric-field electrodes and appropriate electric connecting means.
 15. The combination of claim 13 in which said means for creating a dynamic electric field include a continuous resistive electrode constructed to form a boundary of said dynamic field.
 16. The combination of claim 13 further including means for varying the field parameters of said dynamic electric field.
 17. The combination of claim 16 in which said means for creating a dynamic electric field is constructed to provide a field having an oscillating and a static component and in which said varying means is constructed to vary the amplitude of the oscillating component and the magnitude of the static component both independently of each other and in a manner which maintains a fixed ratio between said amplitude and said magnitude.
 18. The combination of claim 13 in which said measuring means includes an electron multiplier and appropriate electronics for producing suitable output signals associated with the arrival at the detector of the various temporAlly separated charged particle species.
 19. The combination of claim 18 in which said means for measuring the characteristic flight times of said temporally separated charged particle species includes suitable electronic means for measuring the lapsed time between the time of charged particle injection into the dynamic field and the arrival of the various temporally separated charged particle species at said detector.
 20. A device for analyzing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis; means for creating a dynamic electric field within said evacuable vessel, said field being symmetric about an axis, periodic in time, and of a form which acts to accelerate, decelerate and separate charged particles into a first group of species having stable motion in the dynamic field, and a second group of species having unstable motion in said dynamic field, said field also being of a form to provide a component of motion to said charged particles generally parallel to said axis to accelerate, decelerate and to temporally separate said charged particles according to their mass-to-charge ratios and to provide a unique flight time in said dynamic field for each of said stable charged particle species for selected dynamic field parameters; means located adjacent the coordinate origin of said dynamic electric field for periodically introducing charged particles into said dynamic field along said axis of symmetry, said axis of symmetry extending through said introducing means; means for varying the field parameters of said dynamic field; and means for measuring a time of flight of said temporally separated charged particle species that travel in a direction of said dynamic field.
 21. The combination of claim 20 in which said field is of the form phi (x, y, z, t) f(t)( Alpha x2+ gamma y2+ eta z2) where x, y, and z are spatial coordinates, t is time, f(t) is a time varying function, and Alpha , gamma , eta are constants satisfying the relation Alpha + gamma + eta
 0. 22. The combination of claim 21 in which said means for creating a dynamic electric field are constructed to produce an electric potential distribution of the form: where x, y, z are space coordinates, the z-axis of said axis of symmetry, t is time, omega is the frequency of the periodic field, Vdc is the direct current potential, Vac is the amplitude of the alternating current potential, L is the characteristic length of the dynamic field region as measured from the coordinate origin, and R is the characteristic radius of the dynamic field region as measured from the z-axis.
 23. The combination of claim 22 in which said means for creating a dynamic electric field include a plurality of conducting electrodes spaced along said axis of symmetry, and appropriate electric connecting means.
 24. The combination of claim 22 in which said means for creating a dynamic electric field include a continuous resistive electrode constructed to form a boundary of said dynamic field.
 25. The combination of claim 20 in which said measuring means include charged particle detecting means located on said axis of symmetry.
 26. The combination of claim 25 in which said detecting means is positioned such that said introducing means is located on said axis of symmetry between said detecting means and said dynamic field.
 27. The combination of claim 20 in which said charged particle introducing means includes: means for periodically producing charged particles from neutral gas samples; electronic means for controlling the time interval of charged particle production; electronic means for controlling the energy of the charged particles at introduction into the dynamic field; means for selecting the time at which said introduction is initiated when the phase of said oscillating component possesses a selected value; and electronic means for controlling the time interval of charged particle injection into the dynamic field.
 28. A device for analyzing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis; means for creating a dynamic electric field within said evacuable vessel for accelerating and temporally separating various charged particle species according to their mass-to-charge ratios, said field being of the form phi (x, y, z) f(t)(1/Z02)(y2-z2) where x, y and z are spatial coordinates, t is time, f(t) is a time varying function, and Z0 is equal to the length of the dynamic field along the z-axis; means for periodically introducing charged particles into the dynamic field with components of motion both in the x and z directions; and means for measuring the flight times of said temporally separated charged particle species that travel in a direction of said dynamic field.
 29. The combination of claim 28 in which said dynamic electric field creating means includes a plurality of conducting, electric-field electrodes and appropriate electric connecting means.
 30. The combination of claim 28 in which said means for introducing charged particle into said field is located in the vicinity of z
 0. 31. The combination of claim 28 in which said measuring means includes charged particle detection means located in the vicinity of z 0 and is spaced from said introducing means a distance along the x-axis.
 32. The combination of claim 29 further including means for varying the field parameters of said dynamic field.
 33. In the combination of an apparatus for separating charged particles according to their mass-to-charge ratio of the type having an evacuable vessel; elongated electrodes positioned in said vessel and disposed in spaced relationship along a common axis and defining a space therebetween; means for generating a first voltage ( phi ) having an arbitrary periodical function of time f(t); means for supplying said first periodical voltage to said elongated electrodes to establish a first electric field between said electrodes having a time periodical field potential which is a general quadratic function phi f(t)( Alpha x2+ gamma y2- eta z2) of the rectangular coordinates x, y, z of the elongated electrode arrangement, Alpha , gamma , eta being constants satisfying the equation Alpha + gamma eta ; means for introducing charged particles into said electric field between said elongated electrodes so that the forces of said first field are exerted on said charged particles to cause certain charged particles to perform oscillations of a limited amplitude and others to perform oscillations of an increasing amplitude depending on the respective specific charges of the charged particles, the improvement comprising: means for establishing a second electric field in the space between said elongated electrodes, said second electric field having a time periodical field potential having a component in said z direction of said first electric field so that the force of said second electric field exerted on said charged particles between said electrodes cause said particles to oscillate the z-direction whereby the duration of time that said charged particles introduced into said field perform oscillations in the x and y-directions between said elongated electrodes is a function of said second electric field. 34 A device for analyzing and storing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel including means for introducing sample particles into said vessel for analysis; means for creating a dynamic electric field within said evacuable vessel, said field being periodic in time, and of a form which acts to accelerate and separate charged particles into a first group of species having stable motion in said dynamic field, and a second species group having unstable motion in said dynamic field, said field also being of a form to temporally separate said stable species according to their mass-to-charge ratio and to store certain of said stable species; means for introducing charged particles into said dynamic field, said charged particle introducing means located adjacent to the coordinate origin of said dynamic electric field and includes: means for producing charged particles from neutral gas samples; electronic means for controlling the time interval of charged particle production; means for controlling the kinetic energy of the charged particles upon introduction into the dynamic field; means for selecting the time at which said introduction is initiated relative to the phase of said oscillating component; and means for controlling the time interval of charged particle injection into the dynamic field; means including timing means for removing selected stable species from said dynamic field; and means for detecting stable species stored in said dynamic field.
 35. The combination of claim 34 in which said charged particle introducing means is constructed to periodically produce and periodically inject charged particles into said dynamic field.
 36. The combination of claim 34 in which said means for removing selected stable species from said dynamic field is constructed to remove all but one of the selected stable charged particle species from said field.
 37. The combination of claim 34 in which said removing means is constructed to periodically remove selected stable species from said dynamic field.
 38. The combination of claim 34 in which said charged particle introducing means and said removing means are constructed to act together to cause the concentration of a selected stable mass to charge ratio species of charged particles contained in said dynamic field to increase.
 39. The combination of claim 38 in which said detecting means includes timing apparatus and is constructed to cooperate with said removing means to remove said concentration of said stored species after a preselected time.
 40. The combination of claim 34 in which said means for creating a dynamic electric field are constructed to produce an electric potential distribution of the form phi (x, y, z, t) f(t)( Alpha x2+ gamma y2+ eta z2) where x, y, z are spatial coordinates, t is time, f(t) is a time varying function, and Alpha , gamma , eta are constants satisfying the relation Alpha + gamma + eta
 0. 41. The combination of claim 40 in which said means for creating a dynamic electric field are constructed to produce an electric potential distribution of the form: where the z-axis is said of axis of symmetry, omega is the frequency of the periodic field, Vdc is the magnitude of the static field component, Vac is the amplitude of the oscillating field component, the length of the dynamic field region is 2L, and R is the characteristic field radius, and all other quantities are as previously defined, said field also being symmetric through the plane z
 0. 42. The combination of claim 41 further including means for varying the field parameters of said dynamic field.
 43. The combination of claim 42 in which said means for varying the field parameters of the dynamic field is constructed to select different ranges of mass-to-charge species that will demonstrate stable motion and will be contained in this field, and to change the temporal sEparation between various stable species.
 44. A device for analyzing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis; means for creating a dynamic electric field within said evacuable vessel, acting to accelerate, decelerate and separate charged particles into a first group of species having stable motion in the dynamic field and a second group of species having unstable motion in said dynamic field, said field also providing a component of motion to said charged particles generally parallel to said axis to accelerate, decelerate and to temporally separate said charged particles according to their mass-to-charge ratios and to provide a unique flight time in said dynamic field for each of said stable charged particle species for selected dynamic field parameters, said field of the form phi (x, y, z, t) f(t)( Alpha x2+ gamma y2+ eta z2) where x, y, and z are spatial coordinates, t is time, f(t) is a time varying function, and Alpha , gamma , eta are constants satisfying the relation Alpha + gamma + eta 0 and wherein said means for creating a dynamic electric field is constructed to produce an electric potential distribution of the form where x, y, z are space coordinates, the z-axis is said axis of symmetry, t is time, omega is the frequency of the periodic field, Vdc is the direct current potential, Vac is the amplitude of the alternating current potential, L is the characteristic length of the dynamic field region as measured from the coordinate origin, and R is the characteristic radius of the dynamic field region as measured from the z-axis; means located adjacent the coordinate origin of said dynamic electric field for periodically introducing charged particles into said dynamic field along said axis of symmetry, said axis of symmetry extending through said introducing means; means for varying the field parameters of said dynamic field; and means for measuring a time of flight of said temporally separated charged particle species for flight including motion in said dynamic field.
 45. The combination of claim 44 in which said means for creating a dynamic electric field include a plurality of conducting electrodes spaced along said axis of symmetry and appropriate electric connecting means.
 46. The combination of claim 44 in which said means for creating a dynamic electric field include a continuous resistive electrode constructed to form a boundary of said dynamic field.
 47. A device for analyzing charged particles according to their mass-to-charge ratios comprising: an evacuable vessel having means for the introduction of sample particle species into said vessel for analysis, said charged particle introducing means including: means for periodically producing charged particles from neutral gas samples; electronic means for controlling the time interval of charged particle production; electronic means for controlling the energy of the charged particles at introduction into the dynamic field; means for selecting the time at which said introduction is initiated when the phase of said oscillating component possesses a selected value; and electronic means for controlling the time interval of charged particle injection into the dynamic field; means for creating a dynamic electric field within said evacuable vessel, said field being symmetric about an axis, periodic in time, and of a form which acts to accelerate, decelerate and separate charged particles into a first group of species having stable motion in the dynamic field, and a second group of species having unstable motion in said dynamic field, said field also being of a form to provide a component of motion to said charged particles generally parallEl to said axis to accelerate, decelerate and to temporally separate said charged particles according to their mass-to-charge ratios and to provide a unique flight time in said dynamic field for each of said stable charged particle species for selected dynamic field parameters; means located adjacent the coordinate origin of said dynamic electric field for periodically introducing charged particles into said dynamic field along said axis of symmetry, said axis of symmetry extending through said introducing means; means for varying the field parameters of said dynamic field; and means for measuring a time of flight of said temporally separated charged particle species for flight including motion in said dynamic field. 